Re: are there coordinate ionic bonds?

There are several different ways of looking at co-ordinate bonds. Chemists 
generally agree on what a co-ordinate bond is, but there may be differences 
in the exact detail. Let's look at a few examples.

Your question talks about acids. I judge from that that you are familiar and 
comfortable with the Lewis acid view of a co-ordinate bond. Aluminium 
chloride (anhydrous) is not an ionic salt, but a covalent molecular 
compound. And its formula is not AlCl3, but Al2Cl6. One chlorine atom on 
each AlCl3 unit donates both electrons from one of its lone pairs to form a 
new shared electron pair with the aluminium atom from the other unit. This 
completes a stable octet for the aluminium. And the two chlorines involved 
become bridging atoms that join the two AlCl3 units into a single Al2Cl6 
molecule. The two linking bonds are what we call co-ordinate bonds.

Carbon monoxide is an interesting example of quite a different sort. The 
bond in carbon monoxide is a stronger bond than the double bonds in carbon 
dioxide or formaldehyde, and is nearly as strong as the triple bond in 
nitrogen. It is possible to think of the bonding as made up of two ordinary 
covalent bonds, where the carbon and oxygen atoms contribute one electron 
each to shared pairs, and a third co-ordinate bond where the oxygen atom 
contributes both electrons. That leaves a lone pair of valence electrons 
each for the carbon and oxygen atoms to complete stable octets. 
Interestingly, the dipole moment of CO is very small (0.10 Debye). There is 
no significant lone pair component because C and O atoms each have a lone 
pair. The polarization component achieved by the oxygen atom getting the 
greater share of the three bonding pairs of electrons is almost balanced by 
the fact that the oxygen atom has formally had to donate four of the six 
bonding electrons rather than its fair share of just three.

I'll now get around to having a try at your question, which I am not sure I 
fully understand.

What happens if an atom is a very weak Lewis acid? Suppose we were to think 
about sodium chloride instead of aluminium chloride. The usual picture of 
sodium chloride is to suppose that the sodium atom completely gives up its 
electron to a chlorine atom, producing a sodium cation and a chloride anion. 
These ions then cluster together in a crystal lattice, held together by non-
directional electrostatic attraction.

Should we think of sodium chloride in terms of co-ordinate bonding instead 
of or as well as ionic bonding? Perhaps it does not work quite as I have 
just suggested. What if we think of the chlorine atoms donating pairs of 
valence electrons to shared electron bonds with sodium, eventually filling 
up the stable octet of a sodium atom?

It is a nice idea, but it will not quite work. The main problem is that each 
sodium atom is surrounded by six neighbouring chlorine atoms in the sodium 
chloride structure: if the co-ordinate bonding idea were correct, we would 
expect it to be surrounded only by four to make an octet. The magnesium 
chloride (anhydrous) crystal structure also has each magnesium atom 
surrounded by six neighbouring chlorine atoms rather than four.

There probably are ways around this. It might be possible to build up a 
story of bonding around co-ordinate bonds instead of ionic bonds, or some 
sort of hybrid co-ordinate ionic bond. But it would be rather complicated. 
The simple ionic bonding story is short and straightforward, and all of the 
chemist's stories about bonding are only approximations or caricatures of 
the physical reality.